Could not find an implementation of the query pattern for source type

Could not find an implementation of the query pattern for source type ‘Your Type’. 'Select' not found.

In newer versions of C#, the error may look like this:

CS1061: ‘IEnumerable’ does not contain a definition for ‘Select’ and no accessible extension method

Solution:

While the error message might seem confusing, the fix is simple: include using System.Linq; at the top of your file, like this:

using System.Linq;

var list = GetList();

foreach (var name in list.Select(t => t.ToLower()))
{
    Console.WriteLine(name);
}

Once you add this, the compiler will recognize Select() as an extension method from System.Linq, and the error will be resolved.

In newer versions of C#, System.Linq is automatically included by default when you create a C# source file. Additionally, the System.Linq namespace is part of the implicit global usings in recent versions.

However, if you disable implicit global usings (by setting ImplicitUsings to false in your .csproj file), you may encounter this error if your code relies on LINQ extension methods.